1. Field of the Invention
The invention relates to vehicle suspension systems, and more specifically to hydro-pneumatic suspension systems switchable between on-road and off-road configurations. In another of its aspects, the invention relates to a vehicle suspension system adaptable from a configuration emphasizing vehicle ride and roll stiffness to a configuration emphasizing maximum axle articulation. In another of its aspects, the invention relates to a vehicle suspension system capable of raising and lowering the vehicle height in conjunction with multiple configurations.
2. Description of Related Art
Conventional front suspension systems, such as found in light and medium duty pickup trucks, are typically comprised of steel coil springs, shock absorbers, steel roll stabilizer bar, and a 5-bar linkage, or similar arrangement. The rear suspension is typically comprised of steel multi-leaf springs and shock absorbers, or similar arrangement.
While such suspension configurations have very acceptable on-road performance for conventional light and medium pickup trucks, their off-road mobility is hampered by the relative lack of axle roll or tramp articulation when traversing uneven terrain. The front stabilizer bar stiffness and the rear leaf spring stiffness prevent the axles from achieving full tramp movement from the jounce travel limit to the rebound travel limit alternatively side to side, resulting in loss of ground contact when one wheel is traversing a large obstacle, such as a rock or boulder.
For maximum mobility and control over sand, snow, low friction surfaces, and rugged off-road terrain, it is desirable to maintain ground contact with all four tires at all times. Increasing the front and rear axle tramp compliance increases the ability of the tires to maintain ground contact under off-road conditions. However, increasing axle compliance by reducing the axle tramp stiffness to achieve more favorable off-road axle articulation and mobility is limited by deteriorated ride and handling characteristics when the vehicle is driven at higher speeds on normal road surfaces. Off-road mobility is further inhibited by the reduction in ground clearance which occurs when the vehicle is loaded.
It would be advantageous to develop a vehicle suspension system that exhibits the advantages of increased axle compliance for favorable off-road behavior, yet can be made to exhibit the stiffer suspension characteristics desired for on-road performance. It would be further advantageous to develop such a system that provides additional ground clearance when needed, and on command.